The present invention relates to a procedure for re-equipping and simultaneously modernizing an open-end rotor spinning machine comprising
a plurality of spinning stations, PA1 a doffing arrangement which is movable relative to the spinning stations, which doffing arrangement comprises devices for exchanging a full bobbin for an empty yarn-winding tube, PA1 means for interrupting the spinning process of a spinning station for the purpose of a doffing operation, PA1 and at least one piecing arrangement movable relative to the spinning stations, which piecing arrangement is designed to restart spinning with a starting winding already attached to the yarn-winding tube.
Open-end rotor spinning machines of this type have been manufactured by the firm Schlafhorst Autocoro GmbH under the trademark "Autocoro" and are in use all over the world. The principle functions of this open-end rotor spinning machine "Autocoro" are disclosed in U.S. Pat. No. 4,125,990. In the known open-end rotor spinning machine, the doffing arrangement and the piecing arrangement travel independently of one another along the spinning stations. For the purpose of doffing operation, the spinning process is first interrupted at the relevant spinning station. The travelling doffing arrangement then exchanges bobbin of the relevant spinning station for a new empty yarn-winding tube. At a later point, the piecing arrangement travels to this spinning station and sets the spinning process in motion again. This piecing arrangement, which serves also to repair normal end breaks, requires for piecing a starting winding connected to the bobbin. In order that such a starting winding, which permits a piecing process, is also present in a newly applied tube, it is provided in the Autocoro machine that instead of empty tubes, ones with a piecing starting winding are used. Piecing after a doffing operation can thus take place in the same way as the piecing for repairing an end break. This fascinating method has the disadvantage that directly after each doffing operation the new yarn-winding tube comprises a piecing point. Even if such piecing points do not significantly impair the quality of a bobbin, they remain undesirable.
It is an object of the present invention to modernize the known open-end rotor spinning machines already in operation by reequipping them in such a way that the piecing point, in connection with a doffing operation, is omitted.
This object has been achieved according to the present invention in that the piecing arrangement is replaced by a new piecing arrangement which is designed: (i) for doffing operations to piece a starting yarn not connected to the empty yarn-winding tube, and subsequently to attach a newly spun yarn to the empty yarn-winding tube, and (ii) for piecing operations with a partially full yarn winding tube, where previously spun yarn from the yarn winding tube serves as the starting yarn.
This can occur, for example, in that the starting yarn to be pieced during doffing operations is connected to an auxiliary tube located in the new piecing arrangement, and that the auxiliary starting yarn is eliminated after piecing, whereafter the newly spun yarn is connected to the empty yarn-winding tube.
For piecing operations with a partially full bobbin, the starting yarn is taken from the previously spun yarn on the partially full bobbin.
The present invention is based in the first instance on the premise that, if re-equipping does take place, the doffing arrangement can be left where it is, as it is basically irrelevant for this arrangement whether it handles a completely empty new tube, or a new tube comprising a starting winding for piecing. As, however, the starting yarn to be pieced no longer comes from the newly applied tube, but rather from an auxiliary tube located in the piecing arrangement, the empty yarn-winding tube no longer contains the necessary piecing point that was previously the case using starting yarn fixed to the empty tube. This results in an improvement in bobbin quality in so far as that the subsequently full tube comprises one piecing point less than before. When the starting yarn for piecing which is connected to an auxiliary tube is preferably additionally eliminated, for example by means of suction, the result is an additional advantage wherein the piecing point itself places no demands whatsoever with regard to quality. It is sufficient to make a safety piecer, as the piecing point is removed after piecing.
A piecing arrangement, which fulfills the desired requirements is described, for example, in U.S. Pat. No. 5,676,322.
As noted above, the new piecing arrangement and procedure also facilitate piecing in case of yarn breaks with a partially full tube.